Electric discharge devices and high frequency systems therefor



May 22, 1956 E. D. M ARTHUR 2,747,087

ELECTRIC DISCHARGE DEVICES AND HIGH FREQUENCY SYSTEMS THEREFOR Filed Aug. 16, 1950 2 Sheets-Sheet 1 Fig. 2.

Inventor: Elmer D. McArbhuF,

@[IIIIIIIIIMIP- by 4.

- His Attorney.

May 22, 1956 E. D. MQARTHUR 2,747,087

ELECTRIC DISCHARGE DEVICES AND HIGH FREQUENCY SYSTEMS THEREFOR Filed Aug. 16, 1950 2 Sheets-Sheet 2 2 Fig. 7.

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Q U '5} REFLECTOR VOLTAGE E REFLECTOR VOLTAGE I t OT" Elmer D. Mo Arthur;

His Attorney.

United States Patent ELECTRIC DISCHARGE DEVICES AND HIGH FREQUENCY SYSTEMS THEREFOR Elmer D. McArthur, Schenectady, N. Y., assiguor to General Electric Company, a corporation of New York 23 Claims. (Cl. 250-36).

This invention relates to high frequency electrical systems, useful as oscillators, amplifiers, reactance devices and the like, which employ grid-controlled electron discharge devices as elements for controlling the energy within associated resonant circuits. This present appIica tion is a continuation-in-part of my now abandoned copending application, Serial No. 751,358, filed May 29, 1947, and assigned to the assignee of the present application. It is a general object of the invention to provide an improved system characterized by a number of advan tages such as more convenient and relatively wide band frequency control, more convenient amplitude control, and structural simplicity resulting from the fact that the number of resonant circuits heretofore normally required to be associated with the discharge device may be reduced, for example, as by the elimination of the resonant circuits heretofore normally associated with the cathode-grid circuit of the device.

The features of the invention desired to be protected are set forth in the appended claims. The invention itself together with further objects and advantages thereof may best be understood by reference to the following specification taken in connection with the accompanying drawings in which the Figs. 1 and 2 are schematic circuit diagrams employed to illustrate the essential difference in principle of operation between the prior art system of Fig. l and that of the present invention in Fig. 2; Figs. 3 and 4 are graphs indicating certain of the operational characteristics of devices embodying the invention; Fig. 5 represents a practical embodiment of the invention in a simple oscillator; Fig. 6 represents an alternative embodiment of the invention employing the novel frequency and amplitude control means; while Figs. 7 through 12 represent graphically certain operational characteristics of the Fig.. 6 embodiment.

As is well known in the art, it is a common practice to employ multi-electrode electron discharge devices such as triodes having an anode, cathode and control grid as oscillators by the expedient of providing a feedback circuit between an anode-grid resonant circuit and a cathode grid-resonant circuit. The function of such a feedback circuit is to derive a small oscillatory signal voltage from the anode-grid circuit and employ it to energize the cathodegrid circuit in order that oscillations may be sustained by the amplifying effect on that signal voltage effected by the control-grid of the device in the manner well known in the art. Generally speaking, the objects of the present invention are accomplished by eliminating the necessity of the cathode-grid resonant circuit and consequently also the necessity of feedback circuits. In accordance with the principles of the invention, this result may be reached with an oscillator employing a multi-electrode discharge device, such as a triode having an anode, a cathode, and a control-grid and using space charge control of current flow in a manner similar to prior art oscillators, by reducing the high frequency impedance between the grid and the cathode to a very low value, preferably as near to zero as possible, whereby the latter two electrodes are ice maintained at essentially the same high frequency potential during operation. To that end, a large by-pass capacitor may be built into the discharge tube structure between the grid and the cathode. In addition, the interelectrode spacings are chosen to meet specific requirements for electron transit time, which requirements will be indicated more fully hereinafter.

With this arrangement, it becomes possible to generate oscillations with a circuit consisting of a single resonant circuit, such as a cavity resonator between the anode and the grid. Oscillations may be initiated as soon as predetermined minimum voltage is exceeded on the anode of the device. Those oscillations will have a frequency primarily determined by the characteristics of the cavity resonator or other equivalent resonant circuit, and their frequency and amplitude may be further controlled by a unidirectional bias voltage applied to the control grid.

The net result is that an oscillator of considerably simplified construction may be provided which has additionally the advantage that it may be caused to oscillate in a more controllable manner throughout a wider continuous range of frequencies and amplitudes.

The principles of the invention may be better understood by reference first to the schematic circuit of Fig. l showing a feedback oscillator of a type conventional in the art. discharge device such as the triode 1 having a cathode 2, a control grid 3 and an anode 4 enclosed within a suitable evacuated enclosure. Between the anode and the cathode there is provided an output circuit 5 which will generally take the form of a resonant circuit such as a cavity resonator, while between the cathode and the grid there is provided a suitable input circuit 6 which likewise will generally take the form of a suitable resonant circuit such as a cavity resonator. In order that oscillations may be sustained in the entire circuit, a voltage from the output. circuit is fed back to the input circuit through a feedback circuit 7, the energy so fed back being sufficient to maintain a small energy level in the input circuit 6 which by the process of amplification through the triode 1 is caused to sustain oscillations of higher energy level in the output circuit 5. Heretofore, it has been considered essential in practical oscillators that all of these elements be provided in an oscillator, namely, the input circuit 6, the output circuit 5, and the feedback circuit 7 even though in some cases the feedback circuit function may be performed by the inherent interelectrode capacities within the triode, e. g., the capacity between the anode and grid or that between the anode and cathode depending on circuit type. As will be indicated hereinafter, the present invention permits the omission of both the input circuit and the feedback circuit in any form.

Before describing exemplary embodiments of the present invention, it may facilitate the understanding of the operation thereof to consider its theory of operation by comparison with that of the Fig. 1 circuit. The instantaneous current flow through the triode 1 at low frequency may be represented by the following well-known equation:

32 i :K( -E,+e, sin wt) 1 In this equation, 1' is the current flow, EB and Eg repre sent the unidirectional voltages applied to the anode and grid respectively, the quantity e0 sin wt represents the instantaneous high frequency anode voltage, i. e., the voltage across load 5, the quantity 8g sin wt is the instantaneous high frequency input voltage to input circuit 6 derived from the output by means of feedback circuit 7, u is the amplification factor of triode 1, and K is a proportionality constant.

The basic circuit of the present invention may be Such a circuit may comprise a multi-electrode obtained from that of Fig. 1 simply by reducing the high frequency impedance of the input circuit 6 to zero, or as near to zero as practically possible and entirely removing the feedback circuit 7. Such an arrangement is indicated schematically by Fig. 2. In the Fig. 2 arrangement, the input impedance has been reduced to an extremely low value by the introduction of a large bypass capacitor 8 between the grid and the cathode. The output circuit 5 may now be connected between the anode and the grid 3.

With the foregoing changes, the Equation 1 now gives the following expression for the current:

This condition obviously arises because the term 6g sin wt has been reduced to zero due to the fact that the gridcathode impedance has been reduced to zero. Expand ing and neglecting negligible terms, the Equation 2 may, for small values of the term be written as follows:

. e 1=I +Ai sin wt where Io is a unidirectional component and A a proportionality constant for the fundamental alternating component.

It is apparent from the Equation 3 that an alternating component of current can exist in the output circuit even though substantially no high frequency is applied between the grid and cathode. Physically, it can be seen why this should be true since an alternating potential established between an anode and an electrically common gridcathode structure will result in a strong electric field in the grid-anode interspace and a weaker field penetrating the relatively open grid structure to permeate the gridcathode interspace. That is to say, the weaker alternating electric field, which may be termed a primary alternating electric field, at the cathode surface may be viewed as due to electrical lines of force extending through the interstices of the grid and terminating at their opposite ends on the anode and the cathode. Therefore, the alternating field at the cathode surface does not require an impedance between the grid and the cathode in order to exist. This high frequency field at, the cathode will cause a corresponding current variation as indicated by the Equation 3, and it is this current variation upon which the oscillator of the present invention depends for the initiation of oscillation.

Now it is known that at high frequency the discharge tube current tends to lag behind the applied field between the electrodes by a phase angle which is attributable to the so-called transit time phenomena of the electrons. That is to say, because of electron inertia the electrons cannot, at the ultra high time rate of change of the high frequency field, be accelerated or decelerated sufiiciently to keep in phase with the changing field. Otherwise stated, because the electrons have finite velocities, they require a finite amount of time to traverse the space between electrodes, and in so doing they give rise to an alternating current as usual but one having a fundamental frequency component which generally lags in phase with respect to that of the applied field. Thus, wherever the phrases such as electron transit angle are used herein to describe a resultant effect, what is meant is the phase angle of a sinusoidal current or voltage of fundamental frequency referred to another similar current or voltage of the same frequency.

he phase angle due to the transit time phenomena may be represented generally as phi- 71). For the purposes of this discussion, the fundamental component of Equating the two forms given by the Equations 4 and 5, it is apparent that the following equations of phase relationship must be met:

1' A% sin (n t) That is to say, the condition of oscillation can be met if phi (p) is equal to N' times 1r where N is any odd integer. It is thus apparent that the amount of phase lag attributable to the transit time phenomena must equal an odd integral number times the angle or 11' radians. However, in, order to obtain best performance, nearly all of this phase delay should occur in the grid-cathode region in order that the electrons will be as nearly as possible in the desired lagging phase relation at the moment they enter the resonant circuit to which they are to deliver power. With this in mind, the phase delay in the grid-cathode interspace should be considered apart from that in the grid-anode space. if the angular phase delay in the grid-cathode space is called theta sub g (6 and that in the grid-anode space, theta. sub (1 (0a), the proper phase delay is given with fair accuracy by the following approximate expression if the alternating voltages are small as when the oscillations are just starting:

Numcrically the term voltages. If the current How is to be spacecharge limited, it can be determined by the following expression:

0 =9500-7eE';::- radians (9) B 4 y 7t where Sg is the grid-cathode spacing in centimeters and lambda (x) is the wavelength of oscillation.

Then from the requirement that =N1r, it is evident that one of the conditions for starting oscillations is that The average current flow at the start of oscillations can be found from the space-charge equations and Equation 10. This current is:

amps/sq. em. (ll) The foregoing analysis will be understood to represent with workable accuracy only the conditions during the period when oscillations are starting up, i. e., when the alternating components of the total voltage are small compared tothe unidirectional components. After oscillations have built up to substantial amplitudes, their ac curacy will be impaired conslderably by the high amplitudes of the alternating component of voltage.

In Fig. 3, there is shown a vector diagram indicating the phase relationships between the current and voltages involved in the circuit of Fig. 2. The vector iac representing the fundamental component of load current is shown lagging behind the load voltage vector eo by the phase angle N for the voltages given by Equation 10. If some other value of energizing voltages be used, the phase angle and electron transit angle can be made somewhat different, and the current may be represented by some illustrative vector i having an angular position controllable in a preferred manner to be hereafter described to effect tuning by means of the reactive current component ix. Self-sustained oscillations will be maintained so long as vector i is sufliciently far left of the vertical coordinate line to have a negative resistance component i'r large enough to give rise to an amount of negative resistance (equivalent parallel negative resistance) less than any positive parallel resistance in the system. If the amount of negative parallel resistance attributable to i'r is greater than the positive parallel resistance of the system, the voltage e can be sustained only by supplying energy from an external exciting source.

The graph of Fig. 4 indicates qualitatively the form of a typical curve of power output (for one value of N, i. e., one mode) as the unidirectional anode voltage is raised. It will be understood that the oscillating frequency may change in the process due to the introduction of reactive components ix, but in practice optimum power output at a predetermined frequency can be had by proper selection of tube and circuit parameters and voltages as desired. From the curve, it will be apparent that oscillation in the device does not begin until a critical unidirectional voltage (Eb)1 is placed upon the anode. Thereafter, the power output increases until a maximum value is reached after which it decreases to zero at an Eb: (Eb)2. Beyond (Eb)2 the anode voltage is such as to give rise to an alternating current phase angle phi 5) too small to sustain oscillation. It will be understood, of course, that the power and frequency will be similarly affected by variations of the unidirectional voltage applied to the grid and the grid may be used as a means of controlling the average power and the frequency.

Fig. 5 illustrates one practical embodiment of the invention including a novel electron tube structure and an associated cavity resonator circuit in which desired oscillations may be sustained by the operation of the tube in accordance with the aforedescribed principles. It will be noted that the electron tube 9 comprises generally a cathode 10, a grid 11, and an anode 12. The grid and the anode may be supported by generally parallel transverse members 13 and 14 which may be positioned in fixed relation with respect to each other by an insulating cylindrical wall 15 of suitable hermetic sealing materials such as glass or ceramics. For the purpose of supporting and spacing the cathode 10 with respect to the other electrodes, there may be provided on the member 13 a tubular extension 16 to which the insulating wall is sealed. The tubular extension 16 may be closed at its opposite end by an hermetic sealing wall 17 of glass, ceramic or like material through which a cathode supporting tube 18 is inserted and sealed. It will be noted that the upper end of the tube 18 contains the active surface of the cathode which may be, of course, coated with any suitable electron emissive material in the manner well known in the art. For the purpose of heating the cathode 10 to electron emissive temperature, there may be provided any suitable heating means such as the resistor wire 19 which extends outwardly of the tube 18 through an insulating partition 20. The heater wire may be energized by any suitable means such as the battery 21 which forms a closed circuit between the lead to wire 19 and the wall of the tube 18.

In order to provide a substantially zero impedance circuit between the grid 11 and the cathode 10 in accordance with the principles heretofore stated, there may be provided within the extension 16 concentric metallic flanges 22 and 23 on the cathode tube 18 and the extension 16. These flanges may be arranged to have juxtaposed annular portions which form the opposite plates of a capacitor. In between the annular portions there is provided as a dielectric for the capacitor any suitable dielectric material such as the silvered mica washer 24. For one practical tube constructed in accordance with these principles, the capacitor formed by the annular flange portions and the dielectric washer had a capacitance of the order of 50 to 75 micro-microfarads.

Unless care be exercised in design, it may be found that the distributed inductive and capacitative properties of the space defined by the portions of the structure between the cathode 10 and the grid 11' (e. g., the space defined between extension 16 and tube 18) may constitute a gridcathode resonant circuit within the range of normal operating frequencies of the system. That condition will give rise to the possibility that the system may at certain frequencies oscillate as a conventional tuned grid-tuned anode oscillator of the type already described (Fig. 1) and thereby interfere with operation in accordance with the principles of the invention. In order to preclude this possibility, it is desirable that all such grid-cathode interspaces be so shaped that they do not constitute resonant cavities within the desired range of operating frequencies. Thus they are preferably of minimum possible volume whereby they will have natural resonant frequencies greater than any frequency within the desired operating range.

As a suitable cavity resonator for the oscillator, there may be provided a pair of concentric parallel lines constituted by the metallic cylinders 25 and 26. The cylinder 25 is conductively attached to the grid supporting extension 16 as by the spring fingers 27. The cylinder 26 may be connected to the anode by capacitive connections to an annular plate 28 which is arranged to fit over the anode 12 and make resilient contact therewith as by means of the spring fingers 29. The capacitive connection between the plate 28 and the cylinder 26 may be formed by the dielectric washer 30 positioned between plate 28 and annular flange 31 of cylinder 26. It will be understood that this capacitive connection is provided for the purpose of making the high frequency path from the cylinder 26 to the anode of substantially zero impedance while the same path presents a very large impedance of the flow of unidirectional current between the unidirectional voltage sources energizing and biasing the anode and grid, i. e., so that they will not be short circuited for unidirectional currents. It will be understood further that the interspace between the cylinders 25 and 26 will constitute a resonant cavity provided that the space is terminated as by an annular short circuiting member 32 concentric with the cylinders and arranged to make spring contact with the opposite walls thereof. The cavity may, of course, be tuned to any desired natural resonant frequency, corre- -lated with that for which the system has been designed in accordance with the aforedescribed principles, the tuning being accomplished by appropriate adjustments of the short circuiting tuning member 32 longitudinally of the concentric transmission line. To this end, any suitable mounting means such as the rods 33 and 34 may be aflixed to the tuning member. Suitable unidirectional energizing and biasing potentials may be applied to the anode and the grid with respect to the cathode and varied by any convenient means such as the voltage divider 35 having sliding contacts 36 and 37 connected to the grid and an ode, respectively.

It will be understood that the cavity resonator of Fig. ,5

corresponds to the output circuit 5 indicated'in Fig. 2 and that when oscillations are initiated within the system a voltage (20 will appear across the cavity resonator, i. e., between the grid 11 and the anode 12. The voltage applied to anode 12 by divider 35 through contact 37 will be the voltage En indicated in the graph of Fig. it will be apparent. therefore, that oscillations may be initiatcd and sustained by suitable choice of the voltage at contact 37 to lie Within the extreme edges of. the curve in Fig. 4. The effect of the unidirectional grid bias voltage applied by divider 35 through cor ct 36 is indicated by the above equations. The value at the contact 36 will therefore he chose accordingly. The manner in which the interelectrode spacings and the other parameters entering into the foregoing analysis may be adjusted will be. in view of the foregoing description and discus sion, Well u .rsteod by those skilled in the art. Power .nay be c led out the cavity resonator of 5 by means 0! a concentric line 3 having an inner conductor 35', an outer conductor 36 scre cd into a threaded aperture in cylinder 26, and an inductive coupling loop 37.

Thus hit the discussion of the phenomena enabling the attainment of the necessary electron transit angle or phase delay of the fundamental frequency component of the alternating current has been concerned only With the etTect gained by the primary alternating electric field wire construction ore clearly shot a by the plan view This construction is to be distinguished from the wel -known crossed wire or ntesh type of const {ion and comprises a sc of spaced parallel wires 11 of i .1 as tun" en attired to aperby any convenient means such as gold 1 spaced suffieiently to permit the .l ge of electrons through the aperture in (liSl-l 1, ely enough to facili ate the establishment of what may be termed a ma netic feedback as will be more fully ti ribetl hereinarter. it has been observed ti at. ices of the n ention hag the some direct c ent electrical characte t ties. at J n of from 2 to 4 i ser output can be obtained by employi the parall form of grid as shown, 181 than the mesh type.

a other \r the direct current plate voltage, plate eat. amplification factor and trans-conductance may al. but a srbstantial increase of high frequency ized by employing the (hove-do l per l .W cr' zrallel wire a theory of this magnetic lcetlbat phenomena from the utilization of a parallel wire grid as above described is not fully understood. 1 ever. an explanation which seems to be justified by experimental data is as follows.

cs o the invention having a parallel wire grid strated in Figs. 5 and 5. most of the ing throur h the system of parallel currents gives rise to maglines (hence n t the term magnetic feedback") snrrou ng the grid \vi es in closed loops. Consequentlv, a magnetic field may be regarded as forming a sheath ind the arid wires in a direction perpendicular to the the magnetic field lines pass o er the grid Wires ide interspace and form closed loops by c. uath in the grid-cathode interspace. the very h frequencies at which the device of invention is designed to operate, the Maxwell field aticns stipulate that such a magnetic field will give lar to the magnetic field. The component of this electric field appearing in the grid-cathode interspace will accelerate the electrons and produce a cyclic variation of the current just as would an electric field from any other source. This electric field resulting from magnetic feedback may be conveniently called a secondary alternating electric field.

It is believed that the secondary alternating electric field and the primary alternating electric field, mentioned hereto-lore as the electric field which peactrates the grid structure. always additive to give an enhanced electric field Wthin the grid-cathode interspace. The set:- oudttry electric field in arses with fre .cy and becomes quite important at l suencies about to cycles. The secondary field may be considered as creat- 1" an increase in transconductance with a constant am- .ica .or or as creatii a decrease in amplification factor with a constant transcouductance.

6, there is shown an altcrna c embodiment cy and amhereinafter. Except for the Lit.

control electrode, the s3 numerals have therefore been used to do; thrc' The system sion of What may be termed r electrcte 38 positioned on the opposite side of the anode member 12 which in this case may ta ie the form of an open mes. Wire structure for the ting the rez ge the current interstices into the interspnce or re tu 'een the anode and the reflecting ele function of the red sting electrode is to re trollable phase rc WQnship a overshooting the anode 52 into th thereby return them to the anode 173 in phase displacedent with resnect to the portion oi? the tube current in the in erspacc or reaction space bet ecn the grid 1 and the anode As wi l be e'rplaiucd shortly, by proper control of this phase relationship. a certain amount of tuning and amplitu e control may be effected. ci e-ct s: h reflect on to the reflecting electrode with respect to that of the even neg-"five with respect end, any suitable means may be on contact 39 on the voltage divider 35.

The only substantial difference in structure between Pig. 6 Fig. 5 lies in the provision of the reflector e cctrode 38 and of any suitable means for mounting it Within he d schai device. For example it is shown ZlS being taunted upon a lead-in conductor All extending through a hermetic seal 41 Within a central aperture of a transverse supporting member 42. Member 42 may be sealed to a cylindrical conducting Wall 43 which fits into an annular groove 44 within the member 42 and is hermetically embedded therein by the sealing means shown. in this embodiment, the anode is suspended from the member by means of the annular support 45 and may be energized as before by a suitable connection to the transverse supporting member or flange 14 on member 43. in this modification, the grid 11 is similarly supported on transverse member by the cylindrical support 46. a order to obviate any possible tendency of the reflector electrode 38 and its adjacent parts to oscillate at the fre quencies of the system. it may be desirable to provide between electrode 38 and anode a path having low impedance Within the frequency range of the system. Such a path may be provided by a dielectric spacer 47 between a collar portion 48 of electrode 38 and support 45. As with Washer 24, this may form with the latter parts a capacitor of substantially zero impedance. In all other respects, the structure is functionally identical with in corn and in some c'a d that shown in Fig. as, will be apparent to those skilled in the art upon studyv of the drawing. a

In connection with the graph of Fig. 3, it was indicated that a certain amount of tuning could be effected in the oscillator by the introduction of a reactive component of current. In that case, the effect was accomplished by varying the phase relationship between the current and the load voltage e0 by variations of the unidirectional energizing voltage supplied to the anode 12 or the unidirectional biasing potential supplied to the grid 11. The phase change between the current and the load voltage was thereby effected by changes in the electron transit angle characteristics of the current flow.

it will be found that a more convenient method of changing the phase relation of the oscillator current to the load voltage is possible by use of the reflector electrode 38 and by appropriate variations of the unidirectional potential supplied thereto by the voltage divider 35 through the contact 39. In theory, the effect is obtained by permitting a substantial number of electrons of the load current to traverse the interstices of the anode l2 and travel a controllable distance into the reflection space before they are returned to the anode 12 by the decelerating field of the reflection space. It will be understood that by varying the length of the time spent in the reflection path, it will be possible to return the electrons to the anode 12 in any desired phase relation with respect to the main component of load current approach ing the anode 12 from the interspace between the anode and the grid. Generally speaking, for tuning or frequency control purposes, optimum results may be obtained when electrons returned to the anode 12 are substantially in quadrature or reactive phase relation with respect to the main anode current between the grid 11 and the anode 12. In order to effect this, the required transit time of the electrons in the reflection space may be generally stated as being approximately N quarter cycles of the oscillation frequency, where N is any odd integer, and where the transit time is measured as the time required for the electrons to make their excursions from the anode l2 outward into the reflection space and back to the anode 12. Thereby the phase change in the fundamental component of reflected current will equal N quarter cycles (N an odd integer). Where amplitude control of the current at relatively constant frequency is desired, the electronsmaking excursions into the reflection space should for optimum results be returned to the anode 12 in phase with the main anode current or 180 out of phase therewith. The latter phase relationships, whether in or out of phase, may both be referred to as resistive phase relationship. This effect may be accomplished by causing the electron transit time in the reflection space to cause the phase change in the fundamental component of reflected current to equal N half cycles of the oscillation frequency where N is any integer. it will be understood that in order, to obtain the most effective utilization of space within the discharge device and to obtain thereby a device of small proportions, it is important that the distance traveled by the electrons in the reflection space be minimized, that is, that the integer N in the above expressions preferably be small.

The manner of controlling the transit time of the electrons within the reflection space will be well understood by those skilled in the art. Generally speaking, that transit time will be a function of the velocity of the electrons as they proceed through the interstices of anode 12 to enter the reflection space and of the intensity of the decelerating or retarding field set up in the reflecting region by reflecting electrode 38. By appropriately adjusting the potential on the reflecting electrode 38 by means of the contact 39, the latter field intensity may be varied and thereby the transit time of the reflected electrons varied until the desired phase relationship is obtained.

Pig. 7 represents a vector diagram of the current and voltage phase relationships when the reflecting electrode is being employed for tuning purposes. The vector ir represents the current reflected by the electrode 38 while vector iac represents, as in Fig. 3, the current approaching anode 12 from grid 11. While the maximum frequency change will be effected by the vector i1 when it is in exact quadrature relationship to vector lac, nevertheless, for tuning purposes, it will be necessary to vary the angle of the vector z'r slightly on either side of the quadrature relation in order to bring about a desired amount of change in the reactive component irx which, of course, is the component which actually effects the frequency change. This variation, of course, is effected by small variations in the potential on the reflecting electrode 38 one way or the other, depending upon the effect desired. The real component irr will tend to change the amplitude of oscillation. However, it will be found in practice that a sufficient useful range of tuning may be provided by varying the angular relation of the vector ir through only a relatively small range of angles about the quadrature position such that the effect of the real component irr is always substantially negligible. The power output or current can therefore be made substantially constant. I have found in practice that it is possible to effect an appreciable range of tuning in this manner with a relatively negligible change in amplitude. Representative characteristics attained in practice are illustrated by the graphs of Figs. 8 and 9. From these, it will be noted that the frequency can be changed throughout a range of about 20 to 30 megacycles while a corresponding amplitude change of only about 10% is being experienced.

Fig. 10 shows a corresponding vector relation when the reflector electrode 38 is being employed for amplitude control. In this case, the reflected current 1': is indicated by a vector which has a large real component irr 180 out of phase with the current iac. This real component effects a change in amplitude. While the maximum change in amplitude will be effected when vector in is 180 out of phase with iac, it will be necessary to vary the angle of vector it slightly on either side of that position in order to vary the amplitude and that gives rise to a small reactive component irx which will have some tuning effect. However, in practice, I have found that this reactive component can be maintained at a F relatively negligible value insufficient to effect appreciable detuning of the circuit, if the vector ir be permitted to swing through only a relatively small range of phase angles. Despite the small phase angle swing, it is possible to effect an appreciable change of amplitude.- The results thereof are indicated in Figs. 11 and 12 showing representative graphs of performance characteristics which I have been able to obtain in practice. From these, it will be noted that it is possible to obtain a substantial range of amplitude variations constituting about a over-all change in amplitude, while at the same time the frequency of the device remained substantially constant. Power may be coupled out of the resonator of Fig. 6 by means of a concentric line and coupling loop (not shown) in a manner similar to that shown and described in Fig. 5.

Tube structures of the type described in Figs. 5 and 6 together with suitable alternatives therefor are shown and claimed in my copending application, Serial No. 757,164, filed June 26, 1947, and assigned to the assignee of the present invention.

As has been mentioned heretofore, the resonator of the invention is connected to the anode and to the grid and cathode as a high frequency unit. It is preferable, however, for the connection to the grid and cathode to be made on the grid side of the high frequency substantially zero impedance interconnecting the grid and cathode, as shown in the embodiments of Figs. 5 and 6. If the connection is made to the grid rather than the cathode, substantially no high frequency currents flow through the substantially zero impedance or over the cathode structure. This essentially eliminates the possibility of the grid-cathode interspace serving as a resonator or as a portion of the resonator connected to the anode and thereby deleteriously afiecting the operation of the tie vices of the invention. In addition, if substantially all the high frequency currcn flow through the grid structure and such structure is of parallel wire form, the effect of the hereinbefore described magnetic feedback phenomena is greater and hence the operation of the devices of the invention is improved.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus capable of sustaining high frequency elcctrical oscillations at a predetermined frequency comprising an electric discharge device having a cathode, an anode, and a control grid, means connecting said grid to said cathode and having a substantially Zero impednce at said frequency, a resonant circuit tuned to said frequency having one point thereof connected to said grid and cathode as a high frequency unit, said anode being adapted to have imposed thereupon an energizing potential having a value at which the phase of electric currents between said anode and said cathode is displaced by a primary alternating electric field between said grid and. said cathode from the phase of a corresponding high frequency voltage in said resonant circuit to sustain oscillations therein, said control grid comprising spaced substantially parallel wires to permit the fiow of high frequency currents in said wires whereby a secondary alternating electric field is created between said grid and said cathode and said primary electric field is enhanced to increase said oscillations.

2. Apparatus capable of sustaining high frequency electrical oscillations at. a prc te 'mined fre neucy comprising an electric discharge device having a cathode, an anode, and a control grid, means connecting said grid to said cathode and having a substantially zero impedance at said frequency, a resonant circuit tuned to said frequency having one point thereof connected to said anode and another point thereof connected to said control grid, said cathode being connected to said control grid by said substantially zero impedance means so that substantially no high frequency currents flowing in said resonant circuit flow through said substantially zero im' pedance means or over said cathode structure, means for imposing an energizing potential on said anode, said potential having a value at which the phase of electric currents between said anode and said cathode may become displaced i. am the phase of the corresponding high frequency voltage in the said resonant circuit sufiiciently to sustain oscillations therein.

3. Apparatus capable of sustaining hi h frequency electrical oscillations at predetermined frequencies comprising an electric discharge device having a cathode. an anode, and a control grid, means connecting said grid to said cathode and hat g a substantially zero impedance at said frequencies, a resonant circuit tuned to said frequencies having one portion thereof connected to said anode and another portion thereof connected to said cathode and grid as high freq nit, said and said grid being adapted to have imposed thereon energizing potentials having values at which the phase of electric currents between said anode and said cathode is displaced by a primary alternating electric field between said grid and said cathode from the phase of a corresponding high frequency voltage in said resonant circuit to sustain oscillations therein, said control grid comprising spaced substantially parallel wires to permit the fiow of high fre- 1.2 quency currents in said wires whereby a secondary alternating electric field is created between said grid and said cathode and said primary electric field is enhanced to increase said oscillations.

4. Apparatus capable of sustaining high frequency electrical oscillations at predetermined frequencies comprising an electric discharge device having a cathode, an anode, and a control grid, means connecting said grid to said cathode and having a substantially zero impedance at said frequencies, a resonant circuit tuned to said frequencies having one point thereof connected to said anode and another point thereof connected to said control grid, said cathode being connected to said control grid by said substantially zero impedance means so that substantially no high frequency currents flowing in said resonant circuit flow through said substantially zero impedance means or over said cathode structure, means for imposing energizing potentials on said anode and said grid, said potentials having values at which the phase of electric currents between said anode and said cathode may become displaced from the phase of the corresponding high frequency voltage in the said resonant circuit snfficiently to sustain oscillations therein.

5. Apparatus as in claim 4 in which said potentials, the Q of said circuit and the spacings between said cathode, anode and grid are so co-related as to permit said oscillations to be sustained by the electron transit angle between high frequency voltages and currents in said circuit.

6. Apparatus as in claim 4 in which said control grid comprises spaced substantially parallel wires.

7. Apparatus capable of sustaining high frequency electric oscillations at predetermined frequencies comprising an electric discharge device having a cathode, a control grid, an anode, and a reflecting electrode all positioned in that order along an electric discharge path within said device, means connecting said grid to said cathode and having a substantially zero impedance at said frequen cies, a resonant circuit tuned to said frequencies having ,ne portion thereof connected to said cathode and grid as a high frequency unit, said anode being adapted to have imposed thereupon an energizing potential having a value at which the phase of electric currents between said anode and said cathode will be displaced by a primary alternating electric field between said grid and said cathode from the phase of a corresponding high frequency voltage in said resonant circuit to sustain oscillations therein, said control grid comprising spaced substantially parallel wires to permit the fiow of high frequency currents in said Wires whereby a secondary alternating electric field will be created between said grid and said cathode and said primary electric field will be enhanced to increase said oscillations, said reflecting electrode being adapted to have imposed thereupon an energizing potential for re iiecting electric current passing said anode and returning the same to said anode in phase displaced relationship with respect to the phase of said first-mentioned electric currents.

8. Apparatus capable of sustaining high frequency electric oscillations at predetermined frequencies comprising an electric discharge device having a cathode, a control grid, an anode, and a reflecting electrode all positioned in that order along an electric discharge path within said device, means connecting said grid to said cathode and having a substantially zero impedance at said frequencies, a resonant circuit tuned to said frequencies having one point thereof connected to said anode and another point thereof connected to said cathode and grid as a high frequency unit, means imposing on said anode an energizing potential having a value at which the phase of electric currents between said anode and said cathode may become displaced from the phase of a corresponding high frequency voltage in said resonant circuit sufficiently to sustain oscillations therein, and means imposing i on said reflecting electrode an energizing potential for reflecting electric current passing said anode and returning the same to said anode in phase displaced relationship with respect to the phase of said first-mentioned electric currents.

9. Apparatus as in claim 8 in which said control grid comprises spaced wires.

10. Apparatus as in claim 8 in which said potentials on said anode and grid, the Q of said circuit and the spacings between said cathode, anode and grid are so co-related as to permit said oscillations to be sustained by electron transit angle between high frequency voltages and currents in said circuit.

11. Apparatus as in claim 8 including means connecting said reflecting electrode to said anode and having negligible impedance at said frequencies.

12. Apparatus as in claim 8 in which said last-mentioned potential is of such value as to return said secondmentioned electric current in phase relationship having a substantial reactive component and negligible resistive component with respect to the phase of said first-mentioned electric currents.

13. Apparatus as in claim 8 in which said last-mentioned means includes means for varying said last-mentioned potential whereby said reactive component may be varied for varying the frequency of oscillation of said apparatus.

14. Apparatus as in claim 8 in which said last-mentioned potential is of such value as to return said secondmentioned electric current in phase relationship having a substantial resistive component and negligible reactive component with respect to the phase of said first-mentioned electric currents.

15. Apparatus as in claim 8 in which said last-mentioned means includes means for varying said last-mentioned potential whereby said resistive component may be varied for varying the amplitude of oscillation of said apparatus.

16. Apparatus capable of sustaining high frequency electric oscillations at predetermined frequencies comprising an electric discharge device having a cathode, a control grid, an anode, and a reflecting electrode all positioned in that order along an electric discharge path within said device, means connecting said grid to said cathode and having a substantially zero impedance at said frequencies, a resonant circuit tuned to said frequencies having one point thereof connected to said anode and another point thereof connected to said cathode and a grid as a high frequency unit, means imposing on said anode and said grid energizing potentials having a value at which the phase of electric currents between said anode and said cathode may become displaced from the phase of a corresponding high frequency voltage in said resonant circuit sufiiciently to sustain oscillations therein, and means imposing on said reflecting electrode an energizing potential for reflecting electric current passing said anode and returning the same to said anode in phase displaced relationship with respect to the phase of said first-mentioned electric currents.

17. Apparatus as in claim 16 in which said control grid comprises spaced substantially parallel wires.

18. Apparatus as in claim 16 in which said potentials on said anode and grid, the Q of said circuit and the spacings between said cathode, anode and grid are so co-related as to permit said oscillations to be sustained by electron transit angle between high frequency voltages and currents in said circuit.

19. Apparatus as in claim 16 including means connecting said reflecting electrode to said anode and having negligible impedance at said frequencies.

20. Apparatus as in claim 16 in which said last-mentioned potential is of such value as to return said secondmentioned electric current in phase relationship having a substantial reactive component and negligible resistive component with respect to the phase of said first-mentioned electric currents.

21. Apparatus as in claim 20 in which said last-mentioned means includes means for varying said last-mentioned potential whereby said reactive component may be varied for varying the frequency of oscillation of said apparatus.

22. Apparatus as in claim 16 in which said last-mentioned potential is of such value as to reflect said lastmentioned electric current in phase relationship having a substantial resistive component and negligible reactive component with respect to the phase of said first-men tioned electric currents.

23. Apparatus as in claim 22 in which said last-mentioned means includes means for varying said last-mentioned potential whereby said resistive component may be varied for varying the amplitude of oscillation of said apparatus.

References Cited in the file of this patent UNITED STATES PATENTS 1,905,692 Edwards Apr. 25, 1933 2,142,313 Heising Jan. 3, 1939 2,157,952 Dallenbach May 9, 1939 2,451,249 Smith et al. Oct. 12, 1948 2,452,075 Smith Oct. 26, 1948 2,459,806 Fremlin et al. Ian. 25, 1949 2,468,152 Woodyard Apr. 26, 1949 2,532,834 Christenson Dec. 5, 1950 OTHER REFERENCES Pohl, W. J.: Aspects in the Design and Manufacture of Planar Grids for Triodes at U. H. F. Electronic Engineering, London, England, March 1951. 

